A material that is non-electrically conductive in the solid state and electrically conductive in the molten state, such as silicon, can be heated in a susceptor vessel by placing the material in the susceptor vessel in the solid state and inductively heating the susceptor vessel. Heat transfer from the heated susceptor to the solid state material in the vessel will heat and begin to melt the material to its electrically conductive molten state. Electric induction power can then be used to inductively heat and melt the molten material.
In some arrangements two or more induction coils may surround different zones or sections of the exterior of the susceptor vessel with each of the induction coils connected to a separate alternating current power supply. Alternating current from each of the separate power supplies flowing through the induction coils generates the magnetic fields that inductively couple either with the susceptor or the material in the vessel. The generated magnetic fields also create a mutual inductance between the two or more induction coils. In some of these arrangements the outputs of the separate power supplies may be adversely affected by mutual inductance between the two or more induction coils particularly as the material in the vessel melts and the value of mutual inductance changes.
One object of the present invention is to provide an electric power system for electric induction heating and melting of a material in a susceptor vessel when two or more induction coils are provided in an arrangement resulting in mutual inductive coupling between the two or more coils.